Method for the production of a sealing segment, and sealing segment to be use in compressor and turbine components

ABSTRACT

A method is provided for producing a sealing segment for use in compressor and turbine components, by powder injection molding, the method comprising the following steps: a) preparing a first homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent; b) producing a first molded article by injection molding the first mixture; c) preparing a second homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent, the second mixture being selected to exhibit a lower abrasion resistance than the first mixture following a subsequent joint sintering process; d) producing a second molded article as a rub strip by injection molding the second mixture; and e) joining the first and second molded articles to produce the sealing segment. A sealing segment is also provided for use in compressor and turbine components, composed of at least one first molded article as a base element and at least one second molded article having lower abrasion resistance than the first molded article, as a rub strip, the first and the second molded articles each being produced by powder injection molding.

The present invention relates to a method for producing a sealing segment for use in compressor and turbine components, by powder injection molding, as well as to a sealing segment for use in compressor and turbine components composed of at least one first molded article as a base element and of at least one second molded article exhibiting a higher abrasive wear rate than the first molded article, as a rub strip.

Sealing segments of this kind are used, in particular, when working with what are generally known as gap-maintaining systems in the compressor and turbine components. Sealing segments, respectively sealing systems of this kind have the function of maintaining a minimal sealing gap between rotating blading and a housing, as well as between stationary blading and the rotating rotor hubs, and of thereby ensuring stable operating characteristics in the context of a highest possible efficiency. The rotating components of the turbine typically have sealing fins which run in against honeycomb seals in a manner known per se. A honeycomb seal of this kind is described by World Patent Application WO 2004/061340 A1. This known honeycomb seal is made of an individual molded article fabricated by powder-metallurgical injection molding.

The known running-in process can easily lead to overheating of the sealing fins when the contact with the honeycomb material lasts too long or the resistance generated by the rubbing away of the honeycomb structures becomes too great. Therefore, damage to the sealing fins cannot be ruled out in the case of the known sealing segments, respectively corresponding abradable coatings.

It is, therefore, an object of the present invention to devise a method for producing a sealing segment and a sealing segment produced accordingly for use in compressor and turbine components, which, on the one hand, make it possible to inexpensively manufacture a broad array of sealing segment geometries and, on the other hand, to reduce the load that the compressor and turbine components are subject to when running in against the sealing segments.

These objectives are achieved by a method having the features set forth in claim 1, as well as by a sealing segment having the features set forth in claim 16.

Advantageous embodiments of the present invention are described in the respective dependent claims.

A method according to the present invention for producing a sealing segment for use in compressor and turbine components by powder injection molding includes the following method steps in accordance with the present invention: a) preparing a first homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent; b) producing a first molded article by injection molding the first mixture; c) preparing a second homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent, the second mixture being selected to have a higher abrasive wear rate than the first mixture following a subsequent joint sintering process; d) producing a second molded article as a rub strip by injection molding the second mixture; and e) joining the first and second molded articles to produce the sealing segment.

A cost-effective and also individual production of the requisite sealing segments is ensured by using the powder injection molding method. In this context, all injection-moldable and sinterable metals, metal alloys, as well as ceramics may be used for the powder injection molding of the first and second molded articles. Mixtures of the metal powder or ceramic powder are also conceivable. The sinterable ceramics may include nitride ceramics, oxide ceramics and silicate ceramics, as well as carbides, for example. When manufacturing the sealing system according to the present invention, it is critical that the rub strip composed of the second molded article have a higher abrasive wear rate than the first molded article used as a base element and/or fastening element for the sealing segment. Therefore, the present invention makes it possible to satisfy a broad array of material requirements for a sealing segment of this kind in compressor and turbine components. On the one hand, this concerns the simple production of complicated geometries using the powder injection molding method, and, on the other hand, the targeted adaptation of the material selection for producing the first and second molded articles, which may be carried out in conformance with the actual technical conditions. It is thus possible to adjust the properties of the second molded article that pertain to the abrasion characteristics, such as the generation of only low frictional energies and resistances, the effective chip formation and removability of the abraded material, or also that relate to preventing an ignition of the abraded material during grazing contact, in a targeted manner, to the turbine components making grazing contact, such as sealing fins, for example. This clearly lowers the loading of the sealing fins by the grazing contact, for example, thereby making it possible to advantageously reduce the size of the corresponding sealing gap. Moreover, there is no need to use conventional geometries when producing honeycomb seals or honeycomb-structured abradable coatings. Geometries may be developed that are more aerodynamically effective and more cost-effective from a standpoint of production engineering. In addition, the honeycomb structure may be entirely eliminated and, accordingly, planar layers may be produced economically. Furthermore, the present invention makes it possible for the first formed element, which is used as a base element or fastening element of the sealing segment, to be adjusted to the relevant technical and material engineering conditions. This relates, in particular, to temperature resistance and erosion resistance.

In various specific embodiments of the method according to the present invention, the first and second molded articles may be joined immediately following the production thereof and prior to releasing of the same in a joint process. However, it is also possible for the first and second molded articles to be joined following a separate release process and prior to a subsequent joint sintering process that the molded articles undergo. Finally, it is also possible for the first and second molded articles to be joined following a separate release and sintering process that they undergo. In the latter case, mechanical, as well as chemical joining processes are possible.

In other advantageous embodiments of the method according to the present invention, the higher abrasive wear rate of the second molded article is achieved by reducing the metal powder or ceramic powder content in the second mixture. Thus, in the second mixture, for example, the metal powder or ceramic powder content is only approximately 15-30% by volume. As a result, the sintering process yields a porous structure due to a reduction in intergranular contact. Advantageously, no separation effects ensue in the second mixture, and a homogeneous porosity distribution is obtained. There is also no need for any change in the process parameters.

In another advantageous embodiment of the present invention, the higher abrasive wear rate of the second molded article is achieved by using metal powders and ceramic powders having reduced sintering activity. In this context, metal powders having a lower degree of purity, i.e., higher C- and O-concentration may be used, for example. The use of air-atomized, instead of inert gas-atomized metal powder, leads to a higher C- and O-coverage of the surfaces and thus to a reduced sintering activity. Here, the advantage of a very porous structure is derived due to a reduction in the intergranular contact, respectively in the sintering neck formation. Moreover, inexpensive metal powders or ceramic powders may be used. A homogeneous porosity distribution, as well as a reduction in separation effects are achieved. There is again no need for any changes in the process parameters.

In another advantageous embodiment of the method according to the present invention, the higher abrasive wear rate of the second molded article is achieved by admixing binder polymers, which do not entirely decompose during release and/or sintering processes, into the second mixture. In this context, the binder polymers may be selected from the group including the phenolic resins or novolak. Admixing binder polymers advantageously reduces the sintering activity. Carbon residues are produced in the grain interstices of the metal or ceramic powder particles in the sintered product, making it possible to achieve good abrasive wear properties. Advantageously in this case as well, no separation effects occur in the context of a homogeneous porosity distribution.

In another advantageous embodiment of the method according to the present invention, the higher abrasive wear rate of the second molded article is achieved by admixing fillers into the second mixture. In this context, the fillers may be formed from easily cleavable inert materials, such as graphite, bentonite or hexagonal boron nitride and/or from materials which at least partially decompose during the release and/or sintering and contribute to pore formation in the second molded article. Evaporation advantageously takes place during sintering, for example, thereby resulting in a pore formation in the scraping layer, respectively in the second molded article. However, it is also possible that the fillers do not decompose, and that they remain in the sintered product, i.e., in the scraping layer, respectively in the second molded article, in the grain interstices of the metal or ceramic powder particles. Overall, therefore, the result is a quite readily cleavable, respectively abradable rub strip. In addition, the pore formation is optionally effected by surface oxidation in the later use of the sealing segment, for example when graphite is selected as a filler.

In another advantageous embodiment of the method according to the present invention, a multiplicity of homogeneous mixtures of metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent are prepared in accordance with method steps a) through d) to produce a corresponding multiplicity of molded articles and a sealing segment resulting therefrom. Thus, even multilayer sealing segments may be produced cost-effectively in virtually any given geometries.

A sealing segment according to the present invention for use in compressor and turbine components composed of at least one first molded article as a base element and/or fastening element and at least one second molded article having a higher abrasive wear rate than the first molded article, as a rub strip, the first and the second molded articles each being produced by powder injection molding. The at least two-layered design of the sealing segment according to the present invention makes it possible, on the one hand, to adapt the base and/or fastening element, namely the first molded article, as well as the scraping layer, namely the second molded article, both in the geometries thereof, as well as in the material compositions, in a targeted manner to the technical and material engineering requirements. In this context, the sealing segment may be a abradable coating for sealing a radial gap between a rotating rotor blade and a housing of a gas turbine, for example. Moreover, the sealing segment may have a honeycomb design.

In this context, the sealing segment according to the present invention is produced in accordance with a method as described in detail in the preceding.

In another advantageous embodiment of the sealing segment according to the present invention, the sealing segment is made of a multiplicity of molded articles, at least two molded articles being produced by powder injection molding. 

1-20. (canceled)
 21. A method for producing a sealing segment for use in compressor and turbine components, by powder injection molding, the method comprising the following steps: a) preparing a first homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent; b) producing a first molded article by injection molding the first mixture; c) preparing a second homogeneous mixture of a metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent, the second mixture being selected to exhibit a lower abrasion resistance than the first mixture following a subsequent joint sintering process; d) producing a second molded article as a rub strip by injection molding the second mixture; and e) joining the first and second molded articles to produce the sealing segment, the lower abrasion resistance of the second molded article being achieved by reducing the metal powder or ceramic powder content in the second mixture.
 22. The method as recited in claim 21, wherein the first and second molded articles are joined immediately following the production thereof and prior to releasing of the first and second molded articles in a joint process.
 23. The method as recited in claim 21, wherein the first and second molded articles are joined following a separate release process and prior to a subsequent joint sintering process that the first and second molded articles undergo.
 24. The method as recited in claim 21, wherein the first and second molded articles are joined following a separate release and sintering process that the first and second molded articles undergo.
 25. The method as recited in claim 21, wherein the sealing segment is an abradable coating for sealing a radial gap between a rotating rotor blade and a housing of a gas turbine.
 26. The method as recited in claim 21, wherein the sealing segment has a honeycomb design.
 27. The method as recited in claim 21, wherein the metal powder or mixtures of metal powders or ceramic powder or mixtures of ceramic powders include all sinterable metals and metal alloys, all sinterable ceramics, and carbides.
 28. The method as recited in claim 27, wherein the sinterable ceramics are nitride ceramics, oxide ceramics or silicate ceramics.
 29. The method as recited in claim 21, wherein the metal powder or ceramic powder content is 15-30% by volume in the second homogenous mixture.
 30. The method as recited in claim 21, wherein the lower abrasion resistance of the second molded article is achieved by using metal or ceramic powders having reduced sintering activity.
 31. The method as recited in claim 21, wherein the lower abrasion resistance of the second molded article is achieved by admixing binder polymers, which do not entirely decompose during release and/or sintering processes, into the second mixture.
 32. The method as recited in claim 31, wherein the binder polymers are selected from the group including the phenolic resins or novolak.
 33. The method as recited in claim 21, wherein a higher abrasive wear rate of the second molded article is achieved by admixing fillers into the second mixture.
 34. The method as recited in claim 33, wherein the fillers are formed from easily cleavable inert materials, such as graphite, bentonite or hexagonal boron nitride and/or from materials which at least partially decompose during the release and/or sintering process and contribute to the pore formation in the second molded article.
 35. The method as recited in claim 21, wherein a multiplicity of homogeneous mixtures of metal powder or a mixture of metal powders or a ceramic powder or a mixture of ceramic powders and at least one binding agent are prepared in accordance with the method steps a) through d) to produce a corresponding multiplicity of molded articles and a sealing segment. 